As an introduction to problems solved by the present invention, consider the conventional digital tape drive having numerous tracks for the storage and retrieval of data. As the tape passes a tape head, a servo code signal, detected by the head, governs alignment of the head in the center of a particular track. The alignment of the tape and head varies as a consequence of mechanical properties and tolerances of the tape transport and of internal and external mechanical shock and vibration. Voice coil motors support conventional tape heads for maintaining alignment of the head and media in response to the servo code signal. Other conventional devices for audio, video, and data playback and recording also use servo code controlled voice coil motors for alignment of a magnetic or optical head to media formed as tape or disk.
A positioning system based merely on servo code detected from the media is insufficient to meet market demand for convenient, quick, and reliable devices for audio, video, and data playback and recording. Convenience requires ever increasing storage capacity per unit of media. Conventional designs provide increased capacity by increasing track density and consequently decreasing track width, thereby making the process of maintaining alignment more difficult and more expensive. A system that maintains alignment by servo code responds slowly and unreliably when the servo code is corrupted or unavailable. Servo code is primarily corrupted by media and head contamination and defects in the media. Furthermore, servo code is unavailable when the media is not moving because without movement, there is no detected signal.
Conventional systems incur delay to obtain alignment. Before a positioning system that uses servo code can maintain alignment, at least coarse alignment must be obtained. When a stepper motor and lead screw are used in a conventional head positioning system, the stepper motor intrinsically provides information related to current position of the head. However, this information lacks continuous resolution. Additional delays are incurred as a consequence of the masses of moving parts. In addition, reliability suffers from wear.
Devices that playback and record audio, video, and data are commonly incorporated into more sophisticated systems having demanding access time and media capacity requirements. Delays degrade the performance of such sophisticated systems and in some cases reduce the usable capacity of the media employed therein.
Conventional positioning techniques limit media capacity. A considerable length of tape passes across the head in a conventional tape drive as the drive attempts to obtain alignment initially, upon tape reversal, around small defects in the media, and between blocks. Similarly, disk media is fragmented by portions used for obtaining alignment. In each case, media otherwise useful for signal storage is consumed for purposes of obtaining or maintaining alignment.
In view of the problems described above and related problems that consequently become apparent to those skilled in the applicable arts, the need remains in positioning systems for techniques for obtaining head to media alignment in devices for audio, video, and data playback and recording.